The invention relates to a microvalve that is to say a micromechanical valve produced by microfabrication. Microvalves of this type as a rule possesses a multi-layer structure, the individual layers being, dependent on the material thereof, fabricated by etching or molding techniques. Possible designs of such a microvalve will be gathered from the European patent publication 0 485 739 A1 disclosing a plate-like valve member forming a moving component of a valve member layer. The valve member layer is placed between two duct layers possessing input and output flow ducts, whose connection may be controlled by way of moving valve member.
In the microvalve art there is generally the problem that the switching forces most frequently employed and produced by way of actuating means operating on the electrostatic principle of action, are massively reduced by an increase in the electrode spacing. In order to nevertheless provide a sufficiently large switching stroke of the valve member and accompanying high flow rates, large electrode areas, and accordingly large valve member areas, are required. Such large areas do however entail the disadvantage of a substantial sensitivity with respect to pressure differentials between the two chamber parts separated by way of the valve member in the valve chamber, something which may impair the ability of the microvalve to function in a substantial manner.
One object of the present invention is to provide a microvalve, whose sensitivity to pressure differences is reduced to maintain a more reliable manner of operation.
This object is achieved by a microvalve, which comprises a valve chamber, in which a diaphragm- or plate-like valve member is located dividing the valve chamber into two chamber parts, comprising a duct layer placed opposite to the valve member and delimiting a first one of the two chamber parts, such duct layer on its side facing the valve member having an input flow opening communicating with an input flow duct and at least one output flow opening communicating with an output flow duct, such valve member being able to be shifted between a closed position closing the input flow opening and an open position opening the input flow opening and thus rendering possible transfer of fluid from the input flow duct to the output flow duct through the first chamber part, and pressure relieving means effective in the open position of the valve member, such means having at least one expansion recess provided, with at least partial overlap, opposite to the output flow opening on the valve member and permitting an expansion of the transferring fluid, such expansion recess communicating through the valve member with the second chamber part.
It is in this manner that a microvalve is provided, which while having a relatively large area of the valve member moving athwart its direction of extent, is substantially less liable to functional impairment by pressure differentials between the two chamber parts. This is rendered possible in effect since the two chamber parts may communicate with one another fluidwise through the valve member, an expansion recess being provided on the side, facing the input flow opening and the output flow opening, of the valve member of the respective output flow opening, such expansion recess positively influencing the fluid, which flows from the input flow duct to the output flow duct in the open position, and more particularly compressed air, in its flow behavior. Without such pressure relieving means the fluid flowing into the first chamber part would spread out over entire valve member area at a high velocity and cause a rapid build up of pressure between the valve member area and the duct layer, such pressure then constituting a large force opposing any immediately following switching over of the valve member. In the portion opposite to the output flow opening the expansion recess will now lead to an expansion and turbulent flow of the flow which has just been accelerated, something which reduces the flow velocity and favors the flow of the fluid into the output flow duct. Simultaneously the fluid, which is caught or retarded by the expansion recess, is free to pass through the valve member directly to the oppositely placed chamber part so that at this point a counter-pressure, corresponding to the pressure in the first chamber part, builds up and the valve member is at least substantially relieved of pressure or is pressure compensated. A further, following switching over operation can now take place extremely reliably with the existing actuating forces.
Further advantageous developments of the invention are defined in the dependent claims.
Particularly effective, delay-free, relief of pressure takes place if the expansion recess is so designed that the output flow opening associated with it is completely overlapped by it. In this case the mutually opposite openings may hate the same width.
Preferably the expansion recesses are so far spaced from the input flow opening in the direction athwart the switching direction that in the open position direct entry of fluid from the input flow duct is prevented. This ensures that the input fluid is not immediately blasted through the second chamber part to establish a gage pressure which would urge the valve member toward its closed position.
It would be possible to design the expansion recess in the form of a slot-like cutout extending through the valve member athwart the direction of its extent. In order to ensure improved mechanical strength of the valve member however a configuration is however preferred, in the case of which the expansion recess is made like a longitudinal groove, it communicating via at least one relief duct, which extends through the valve member, with the second chamber part. Instead of a single relief duct it is possible as well to provide a plurality of expansion ducts, which open into the expansion recess with a spacing between them. Despite the presence of the connecting ducts extending through the valve member, there is accordingly a design of the valve member which is resistant to bending and twisting, something which in particular also promotes cooperation between the valve member and the opening to be closed in the closed position.
A particularly advantageous design of the microvalve possesses a linear, slot-like input flow opening, which on both longitudinal sides is flanked respectively by an output flow opening, also having a longitudinal form and aligned in parallelism, each output flow duct being opposite to an expansion recess provided on the valve member. The input fluid is therefore able to spread out in the first space part toward opposite sides, it however being retarded after only a short travel in the above mentioned manner and being caused to flow into the output flow ducts and the second chamber part.
In order to improve the pressure relieving effect even farther the design may be such that, as related to the transfer direction of the fluid, an expansion recess is followed by one or more additional expansion recesses, which although same do not have any output flow opening opposite to them, nevertheless communicate also with the second chamber part and compel flow of the fluid, at the preceding expansion recess, to the opposite second chamber part in a similar manner.
A particularly advantageous design of the valve member, which unites satisfactory flow behavior with high mechanical strength and also manufacturing advantages, is such that in both valve member areas there is respectively a group of mutually parallel groove-like recesses, the recesses of the two groups extending transversely in relation to each other and having a depth such that at points of intersection they merge with one another, at least one expansion recess and, if necessary, at least one additional expansion recess being a component of the recesses associated with the first chamber part.
The second chamber part is delimited by a further layer opposite to the valve member, such further layer being in the form of a ductless covering layer, or of a further duct layer containing at least one fluid duct, dependent on the type of valve.
In the following the invention will be described in detail with reference to a working example depicted in the drawings.